The proposed studies will focus on the general topic of blood- tissue exchanges of various diffusible substances across the pulmonary capillary bed, with emphasis on evaluating changes associated with various degrees of pulmonary edema. We are particularly interested in defining the accuracy and sensitivity of the tracer-dilution method for measuring pulmonary blood volume (PBV) and extravascular lung water (EVW) in normal and edematous lungs. It appears, from our previous studies, that tracer-dilution estimates of EVW reflect the status of lung perfusion (vascular recruitment) but do not correlate well with actual tissue water content. Therefore, we propose the development of an independent method for making serial measurements of PBV and EVW based on quantitative changes in roentgen opacity of the lung (roentgen videodensitometry). This technique will permit us to correlate changes in distribution of pulmonary blood volume with accumulation of edema fluid in different segments of the lung, and it will provide a quantitative basis for comparison and interpretation of tracer-dilution estimates of PBV and EVW. Additional studies will be directed to the measurement of pulmonary capillary permeability to various hydrophilic diffusion-limited tracers. Permeability-surface area (PS) products will be calculated from venous tracer-dilution curves following simultaneous intra-arterial injection of combinations of non-diffusible (reference) and diffusible tracers. Ratios of PS products will provide estimates of relative capillary permeability to various diffusible tracers of interest. Measurements made in edematous lungs will be compared with previously defined normal values in non-edematous lungs in order to detect any changes in capillary permeability associated with the development of pulmonary edema.